Christine Schulz has never visited England, but she speaks with the clipped inflection of a vaguely British accent. It’s not an affectation but, rather, the mystifying after-effect of an 18-hour surgery she endured in 2009 to remove about half her tongue due to a cancerous growth that had spread to her lymph nodes.

Surgeons used skin from her wrist and upper leg to re-create the missing portions of her tongue. Through long term speech therapy, Schulz, 47, of Hollister, Calif., re-learned how to eat and talk with her reconstructed tongue. If she sounds as if she’s from a different country, Schulz isn’t complaining.

“At the moment I woke up from surgery, I realized exactly what a huge deal it was,” she said, describing how she had an incision in her throat to allow her to breathe and was prohibited to speak in her earliest days of healing.

Oral cancers, which include those of the mouth and tongue, are most common in men over 60 with a long history of smoking or chewing tobacco, often combined with heavy drinking. But in recent years, a spike in the incidence of oral cancers is being attributed to human papilloma virus or HPV.

But Schulz’s cancer was neither HPV– nor tobacco-related. That puts her in a camp of fewer than 7 percent of all oral cancers that have no identifiable cause, according to the Oral Cancer Foundation, an advocacy group based in Newport Beach, Calif.

“Surprisingly, a high percentage of tongue cancers — 45 percent — is not related to the virus. The cause, we don’t know,” said Dr. Steven Wang, a head and neck surgeon at the University of California San Francisco with expertise in microvascular reconstructive surgery.

Tongue cancer is relatively rare, diagnosed last year in about 13,000 U.S. patients — more than 9,000 men and 3,700 women. It leads to some 2,000 annual deaths, according to the National Cancer Institute. Overall, there were 42,000 diagnoses of the broader category of oral cancers, which include the mouth cavity, lips and the oropharynx, or the part of the throat at the back of the mouth. Oral cancers combined kill about 8,000 each year.

While statistics show many cancer types leveling off or even decreasing in recent years, the incidence of oral cancer has increased, due in large part to HPV. Between 1988 and 2004, the percentage of HPV-related oropharynx cancers skyrocketed by 225 percent, according to a 2011 study published in the Journal of Clinical Oncology. But that doesn’t explain the rise in oral cancers among patients with no known cause.

“It could be a genetic predisposition or it could be an outside source, a causal agent that hasn’t been discovered yet,” said Brian Hill, the Oral Cancer Foundation’s executive director.

Wang, who reconstructed Schulz’s tongue, said nonsmoking-related oral cancers tend to be less responsive to chemotherapy and radiation than HPV- and smoking-related tongue cancers. And often the symptoms are overlooked. His latest research, to be published in the journal Otolaryngology — Head and Neck Surgery, found that former or current smokers with a form or tongue cancer called squamous cell carcinoma had a better chance of surviving than patients with the same cancer who never smoked.

“People always notice the sore or the ulcer in the mouth, but they’re not thinking it’s cancer,” he said. “They’re thinking, ‘I’ve never smoked, I’m too young.’ And, unfortunately, their doctors are thinking the same thing.”

Because treatment is frequently delayed, Wang said nonsmokers with tongue cancer are more likely to have the disease treated aggressively. Surgeons are able to reconstruct the tongue, but they have yet to find a way to re-create its function.

For Schulz, what started as a bump in the back of her tongue that wouldn’t go away turned into a life-altering experience. Her marathon surgery and reconstruction was followed by chemotherapy, radiation and a year and a half of speech therapy.

Most extremely sweet foods do not register on what’s left of her taste buds, although she loves chocolate more than ever. She avoids bread and crackers because those kinds of foods turn to cement in her mouth, and she finds salads just too much work.

“Putting food in my mouth still feels foreign,” she said, adding that it takes her a long time to eat. “I have to chew it. I have to have a thought about where it is inside my mouth and make sure it stays there, chew enough so I know I have to swallow and then I have to have water.”